Nectar is a sugar-rich liquid produced by plants. It is produced either by the flowers, in which it attracts pollinating animals or by extrafloral nectaries, which provide a nutrient source to animal mutualists providing anti-herbivore protection. It is produced in glands called nectaries.

Nectar is an economically important item, the sugar source for honey. It is also useful in agriculture and horticulture because the adult stages of many predatory insects, as well as hummingbirds and butterflies, feed on nectar.

Floral nectaries are generally located at the base of the perianth, so that pollinators are made to brush the flowerâ€™s reproductive structures, the anthers and pistil, while accessing the nectar.

Nectar produced outside the flower is generally made to attract predatory insects. These predatory insects will eat both the nectar and any plant-eating insects around, thus functioning as â€˜bodyguardsâ€™. Extrafloral nectaries are generally located on the leaf petioles, mid-rib or leaf margin. They are thought to be modified trichomes and exude nectar from phloem sap. Extrafloral nectaries can be found on species belonging to (amongst others) the genera Salix, Prunus and Gossypium. In many carnivorous plants, nectar serves to attract insect prey.

Although its main ingredient is fructose or natural sugar, nectar is a brew of many chemicals. For example, the nicotiana attenuata, a tobacco plant native to the US state of Utah, uses several volatile aromas to attract pollinating birds and moths. The strongest such aroma is benzyl acetone, but the plant also adds bitter nicotine, which is less aromatic and therefore may not be detected by the bird until after taking a drink. Researchers speculate the purpose of this addition is to drive the bird away after only a sip, motivating it to visit other plants to fill its hunger, and therefore maximizing the pollination efficiency gained by the plant for a minimum nectar output. Presence of neurotoxins such as aesculin are present in some nectars such as the California Buckeye.